The present invention relates to a process and apparatus for automatically applying a quantity of heat energy sufficient to achieve a desired temperature at a given location prior to a period of usage, especially for preheating an automotive vehicle. However, the invention is also applicable to other situations where automatic preheating would be desirable, for example for internal combustion engines serving for driving machines at building sites, which engines are to be preheated at the start of operation, or similar purposes.
Preheating systems are known (Webasto "Technische Mitteilung" [Technical Report] E 2-10) wherein the heater is turned on prior to an intended period for commencement of its utilization for a time period that is estimated and set beforehand. The maximum preheating period is one hour. If a relatively high outside temperature will supposedly prevail during the time of use, for example for the intended start up time of an automobile, then according to data obtained from experience, a substantially shorter preheating time will be set. Thus, for a correct estimation of the turning-on time, a certain amount of experience is required which, however, leads to erroneous results should weather conditions change considerably after setting the timer clock and before the set time for commencement of preheating has been reached. If severe freezing occurs in the meantime, the set preheating time will be too short, and the preheating result will be unsatisfactory. On the other hand, if conditions become mild, too long a preheating time will be utilized, with the outcome that an unnecessarily high temperature will be reached and an inordinately high amount of energy consumed.
It has been known (German utility model 1,765,291), in order to limit energy consumption, to install in a heater circuit a two-position controller that is responsive to temperature and which will cut off application of heat once a desired temperature has been obtained. However, if this control method is to be effective in the case of suddenly occurring cold, then the maximum preheating time must be set; after attainment of the desired temperature, which occurs earlier or later dependent on the actual weather conditions, the controller turns off any further heating. But this procedure still leads to a considerable squandering of energy, since equipment to be heated up, especially in automobiles, are not thermally insulated so that the cutting in of the preheating feature that will be too early in most instances, has the result that the equipment is maintained at the desired temperature for an unnecessarily long time period prior to utilization, and heat and energy is wasted due to its transmission to the environment.
Accordingly, it is an object of the present invention to be able to obtain a desired preheating result with a minimum energy consumption and with maximum safety. This object has been obtained in accordance with a preferred embodiment of the invention by a process wherein the preheating times required to achieve a desired temperature for various possible actual temperatures at a given location are determined, at a predetermined point of time prior to a preset utilization commencement time, a correct preheating time for use based upon actual temperature conditions is automatically selected from those preheating times previously determined, and then application of heat is automatically commenced at the given location at a time prior to the usage commencement time corresponding to the difference between the usage commencement time and the correct preheating time. This method according to the present invention can advantageously be carried out in accordance with a preferred embodiment of the apparatus of the present invention which includes a heating device, a presettable timer actuated switching control means for actuating the heating device, and actual temperature value sensing means for sensing the actual temperature at the location of usage and a memory unit that is addressable in dependence on the actual temperature values sensed by the sensor means and containing as stored data, preheating times to be read out corresponding to the respectively required heating time necessary to achieve the desired temperature for each of the various possible actual temperatures at the usage location. The switching control means is operable to actuate the heating device at a time prior to the preset time for commencement of usage that corresponds to the difference between the preset usage commencement time and the stored preheating time read out by the memory unit based upon the actual temperature values at the point of time prior to the preset usage commencement time.
Thus, instead of preprogramming a given turn-on time for a heating device as done in the prior art, as noted above, a preset instant at which a period of usage is to be commenced is preset, whereupon (within a suitable maximum time limit of, for example, one hour) preheating then is initiated on the basis of variables determined empirically before hand and the sensed actual temperature conditions so that the desired temperature is obtained precisely the instant the equipment is intended to be put into use.
Especially in the case of forced circulation heating systems, the procedure can be such that, at a predetermined time interval, for example, one hour before the respectively programmed usage commencement time, the actual temperature, for example, the temperature within the passenger space of a automotive vehicle, is measured and independence thereon, the turning-on time of the heater is predetermined with the aid of an arithmetic algorithm so that, at the intended instant at which usage is to be commenced, the desired temperature level will have been obtained. In this connection, it is particularly advantageous if the preheating times are determined on a basis of the time required by a given heating device to overcome a temperature difference between the various possible temperatures at the given location of usage and the temperature desired to be achieved at the commencement of usage and these preheating times are committed to storage.
Under circumstances wherein a preheating requirement may have to be especially intense, several heating stages can advantageously be utilized in accordance with the present invention, one of these heating stages being selected on the basis of a relay system at the time of presetting, or is adjusted automatically by a thermal probe. However, in general, a single preheating stage will suffice for constructional simplification, especially if the heat distribution period in the equipment to be preheated is relatively brief since, in such a case, there results only a brief period.
Selectively, the respective internal temperature or temperature difference (external-internal) may be utilized in accordance with the invention to determine the start of preheating and can be the temperature or temperature difference prevailing at the time at which preheating is commenced; alternatively, the temperature or temperature difference can be constantly controlled in order to readjust the turn-on time if heating up occurs too rapidly, for example, if the equipment is exposed to strong sunlight during preheating, so that the preheating unit is cut off and then reactivated later on. In the event that utilization of the equipment is not actually commenced at the preset usage commencement time, the temperature achieved during preheating can be subjected to regulation at a constant value after the desired temperature has been reached, i.e., after the preset usage commencement time is reached, a conventional two-position control is activated. In the case of heaters that operate with fresh air rather than re-circulated air, it is especially suitable to determine the preheating times for overcoming of the temperature difference between the actual temperature at the usage location and the desired temperature in dependence upon various possible ambient temperatures. Thus, in this instance, it is not only the actual temperature in the equipment to be heated, e.g., in the automobile, which is of importance, but also the outside air temperature which can differ, prior to start up of the preheating process or during the preheating period, from the actual internal temperature.
In accordance with the apparatus aspect of the present invention, the memory may utilize various appropriate devices of very different design of types that are known per se. In particular, it is contemplated that the different thermodynamic characteristics of different large equipment pieces to be preheated by the apparatus can be stored as respective time constant correction factors which, in the simplest case, may be a waiting variable that is settable with the aid of a multi-stage switch for the specific equipment involved. This waiting variable determines the turning-on time, coupled with the determined actual temperature or the determined temperature difference.
In accordance with a further feature of the present invention, in the case of an automobile heater preheating apparatus including an external temperature sensor, an ice warning signal can advantageously be connected therewith for indicating that the external temperature is low enough that roads might be icy. If a digital clock is present, its display can preferably be utilized for the ice warning indicator.
Additionally, the apparatus according to the present invention can utilize a timer for setting the usage commencement time that is able to provide switching between different time intervals without resetting of the specific time of usage commencement, for example, so as to enable preheating to commence at a given time every 24 hours during the week and then with a longer interval elapsing, when desired, for purposes of spanning weekends and vacations. Such long term programming is practical since the weather conditions during any subsequent period of usage need not be predicted.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.